dj06482 GRM+ Memberand Dork
8/6/14 9:08 a.m.

I'm going up to my parent's house tomorrow to help out my Dad diagnose a stuck caliper on their '94 C4 Corvette. (Their car has the base suspension, and therefore the JL9 12" front brakes, not the Heavy Duty J55 brakes). My dad noticed a burning rubber smell after driving the car a few miles, and on further inspection, the driver's side wheel is much warmer than the passenger side wheel. The car is stock, and the brakes haven't been touched since they've bought it 11 years ago.

From some quick research, it seems like the things that can cause this issues are:

1) Caliper slides not greased (they haven't been touched in 11+ years)
2) Rubber lines deteriorating (they're 20 years old)
3) Caliper needs to be rebuilt/replaced (ditto on being 20 years old)
4) ABS block (fluid flows from the master to the ABS)

My plan of attack is to take the pads out, check their condition, and re-grease the slides. I have a new set of rotors/pads that can go on if needed. I've read the part about the front caliper bracket bolts that attach the caliper bracket to the knuckle need to be torqued to 165 ft-lbs (+/- 15 ft-lbs) and they need to be cleaned and have blue threadlocker applied. The caliper bolts up front have a 22-25 ft-lb torque value.

I'm also thinking that flushing the ancient fluid is probably a good idea. I've seen that the order seems to be RF, RR, LR, LF based on the fact that the fluid goes from the master cylinder through the ABS module, and then to the individual wheels.

My dad has a shop manual that I bought him, so that should help with some of the steps.

Any other recommendations from the C4 crowd?

Thanks in advance!


novaderrik PowerDork
8/6/14 12:24 p.m.

i always diagnose a stuck caliper by starting at the master cylinder and unhooking fittings towards the caliper until the pressure releases.. that being said, it's probably the hose...

i'm trying to remember how the calipers are set up on those cars- i had C4 front brakes on my Nova, but i don't remember any bolts that you'd want to get anywhere near 165 lb/ft of torque... if i recall correctly, the pads fit into the grooves in the basket, then the caliper slides over them and is held in place by a couple of small bolts that hold it to the pads, with nothing connecting the caliper itself to the bracket.

Gearheadotaku GRM+ Memberand PowerDork
8/6/14 12:28 p.m.

165 LBS has got to be some sort of misprint. The bracket to the knuckle is tight, but I don't think it's that tight. The caliper is held with a pin and clip, no bolts and very little to lube. I'd flush the system and swap the out both front hoses first, then the caliper. While the pads are the same, the "12 and "13 (J55)brake pkgs use different calipers.

dj06482 GRM+ Memberand Dork
8/6/14 12:42 p.m.

Thanks for the feedback - I edited my initial post to be more clear. The bolts with the 165 ft-lb value are those that attach the caliper bracket to the knuckle. The torque values varied over the years, from something like 131 ft-lbs for early C4s up to 165 ft-lbs (+/- 15 ft-lbs) for the later years.

Here are the bolts I'm talking about:

 photo C4CorvetteCaliperBolts_zpsfaf7a394.jpg

conesare2seconds HalfDork
8/6/14 1:43 p.m.

You are probably on the right track. Greasing the caliper pin is an easy fix and the most likely solution.

dj06482 GRM+ Memberand Dork
8/6/14 1:50 p.m.

Ordered up the two front hoses. They could stand to be replaced after 20 years.

One thing that's been slightly frustrating with this project is parts availability. NAPA was unable to source calipers at all (so I decided to wait), and they weren't able to get brake lines to me in a short amount of time. I'd love to support a local business who can get me parts more quickly than an online vendor, but Rock Auto can get the parts to me quicker. The brake pads, rotors, and hardware kit that I ordered on Monday from Rock Auto was at my parent's house by 9:30 AM the following day. Hoping I can get the brake lines almost as quickly, we'll see.

dj06482 GRM+ Memberand Dork
8/8/14 9:37 p.m.

Bump for an update. I took a look at it today, both the driver's and passenger's side front caliper pins were dry as a bone and had corrosion on them. I was going to take a picture of them, but my Dad cleaned them up with an emery cloth before I could get to my phone. Replaced the pins with new pins, washers, and circlips. I greased the pins with Syl-glide, and reinstalled everything. Pads had over 50% left, and the calipers looked good.

After servicing, both wheels spun easily after applying the brakes a few times to ensure the pads were seated near the rotor. Took a 15 mile drive and wheel temps were cool, although the driver's side wheel does seem to have more heat coming from the engine bay than the passenger's side. My parents will take some slightly longer trips with it this weekend, but so far so good.

Thanks for all your advice and feedback!

patgizz PowerDork
8/9/14 8:38 a.m.

yeah those pins corrode even on a car not driven in any kind of weather. mine were nasty and the car has never seen salt and stays indoors most of the time.

dj06482 GRM+ Memberand Dork
8/11/14 7:16 a.m.

After an extended drive on Sunday, the verdict was that replacing the pins and greasing them did the trick. I'm pretty confident that simply cleaning and re-greasing the pins would have worked, as well, but since I had the new pins I figured I'd use them to eliminate any possible issues.

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